Filters of the above-mentioned type are used, i.e. for permanent or temporary implantation in the vena cava, in particular the inferior vena cava, to prevent thrombi or emboli from reaching the patient's lungs and causing pulmonary embolization.
Such filters are well known in the art, e.g. from U.S. Pat. Nos. 3,952,747, 4,425,908; 4,619,246 and 5,324,304 as well as published European patent application No. 430848.